Automatic-telephone-exchange system.



PATENTED MAR. '7, 1905. J. K. NORSTROM & H. M. GRAIP.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAY 18, 1903. RENEWED JULY 5. 1904.

3 SHEETS-SHEET- 1.

RN NH m m ,0 m 4W e r 5 z 7% K 3M m a E: $5.5. 5525 33m Q E. Q

No. 784,498. PATENTED MAR. '7, 1905. J. K. NORSTROM 6/: H. M. GRAIF.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAY 18, 1903. RENEWED JULY 5. 1904.

d'draas 15, in

ahnzzifiy'fiif I LEenr aK G g w [18,, 3M MW No. 784,498. PATEN'ILD MAR.'7. 1905. J. K. NORSTROM & H. M. GRAIP.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLIUATIOH FILED MAY 1a, 1903. BEHEWED JULY 5. 1904.

s SHEETfi-SHBET s.

UNITED STATES Patented March '7', 1905.

PATENT OEETC JOHN K. NORSTROM AND HENRY M. GRAIF, OF CHICAGO, ILLINOIS,ASSIGNORS TO AUTOMATIC TELEPHONE COMPANY, OF CHICAGO, ILLINOIS, ACORPORATION OF- ILLINOIS.

AUTOMATlC-TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 784,498, dated. March'7, 1905.

Application filed May 18, 1903. Renewed July 5, 1904. Serial No.215.393.

To t 11/71/0111, it warty concern.-

Be it known that we, J OHN K. NORSTROM and HENRY M. GRAIF, of Chicago,in the county of Cook and State of Illinois, have invented certain newand useful Improvements in Automatic-'lelephone-Exchange Systems; and wehereby declare that the following is a full, clear, and exactdescription thereof, reference being had to the accompanying drawings,which form part of this specification.

Our invention relates to automatic-telephone-exchange systems whereinthe various functions of a telephone-exchange incident to the operationof connecting for intercommunication the lines of two subscribers areautomatically performed.

One of the objects of our invention is to provide a system wherein for aswitchboard accommodatinga given number of subscribers say one hundredarelatively small nmnber of line-selecting switches-say ten-may beemployed and to so arrange the switches with reference to auxiliarydevices and the lines that any switch may be controlled and actuatedfrom any line.

A further object of our invention is to so arrange the switches andauxiliary devices relative to the lines of the subscribers that at anytime any subscriber can control only the first idle or inactive switchand that when any switch is in service for one subscriber said switch ispositively removed from the control of any other subscriber, the firstthen idle switch, however, being automatically brought within thecontrol of the other subscribers.

A further object of our invention is to provide a system wherein theactuating mechanisms of the various devices are placed in circuitsauxiliary to the talking-circuit, so that said talking-circuit whenestablished between two subscribers stations contains no localresistances, such as relay-coils or other impeding devices, in series insaid circuit within the exchange.

Numerous other desiderata of automatic-exchange telephony areaccomplished in the use of our invention which one will not here seek toenumerate, but which will become apparent to those skilled in the artfrom the disclosure made in the following specification and claims andthe accompanying drawings.

In the drawings, wherein we have illus trated our invention as appliedto a centralenergy telephone-exchange, Figure 1 is a diagrammaticillustration of the stations of two subscribers, the line-wires of saidsubscribers being so related that when the intersection-line Y Y of saidfigure is coincidently superposed on line Y Y of Fig. 2 said wires formconnections with the corresponding wires intersected by line Y Y of Fig.2. Figs. 2 and 3 are continuing views diagrammatically illustrating thecentral mechanism of an automatiocxchange system, it being understoodthat the wires intersected by the broken line V V of Fi 2 are continuedfrom the colresponding points intersected by the line V V of Fig. 3.Fig. 4 is an enlarged detail of the switch mechanism diagrammaticallyillustrated in Fig. 3, the wiring of Fig. 4. being so arranged that itcorresponds with that of Fig. 3 wl1en;su pol-posed upon Fig. 3 with thedotted lines XX of the respective ligures coincidentally placed.

Referring now first to Fig. 1, station No. 1 and station No. 2 areillustrated as equipped with apparatus similar in every respect, so thatit will be necessary only to describe a single station, it beingunderstood that the equipment is duplicated at every other station. Atstation No. 1. 5 indicates a receiverhook; 6, a receiver; 7, atransmitter; 8, a polarized bell, and 9, 10, and 11 represent threeeircuitchanging keys suitably associated with the subscribers set. Thesekeys we will for convenient reference arbitrarily designate as follows:9 the primary-impulse key, 10 the switch-operating key, and 11 theconnecting-key. The three keys are illustrated as simplecircuit-changing keys, each havingaspring-leaf arranged to play betweenan upper and a lower contact and each normally closing a circuit throughits upper contact. In practice of course other mechanism may beemployed; but we prefer to herein illustrate our invention in itssimplest asconnected to earth, as by taps 9, 10, and 11,

respectively, to a common ground-wire 12. The key 11 is connected to theupper contact of key 9 by wire 11", so that when said key 9 is in normalposition the key 11 is connected to the line-wire Z.

The telephone devices are wired as follows: From the upper hook-contactextends the wire 13, including in its circuit the primary p of aninduction-coil and the transmitter 7 and terminating in the uppercontact-point of the key 11. A tap 14, taken from said wire 13,includesthe polarized hell 8 and terminates in the lower hook-contact. The hookis permanently connected by wire 16 with the upper contact of key 10.The receiver 6 is included in a closed circuit 6, also including thesecondary j) of the induction-coil inductively associated with theprimary of said coil. 15 indicates a tap from wire 13, extending to asecond lower contact of key 11 and preferably including in its circuit aresistance 15.

It will be apparent that with the arrangement described when thereceiver is upon the hook, as illustrated at station No. 2, the bell iscut into the line-circuit and the transmitter excluded from said circuitand that when the receiver is removed from the hook, as illustrated atstation No. 1, the bell is cut out of circuit and the transmitter 7included there- It will also be apparent that the depression of any oneof the three keys 9, 10, or 11 grounds the line on one side or the otherand cuts out all of the telephone instruments.

Referring now to Figs. 2 and 3, which illustrate the apparatus employedat the central station for automatically connecting the lines of any twosubscribers for communication upon the proper actuation of the devicesat the station of the calling subscriber, the incoming pairs of linesare indicated at L L L, &c., to correspond with their respectivestations Nos. 1, 2, 3, &c.

WVe have chosen to illustrate our invention as embodied in a switchboardequipped for five subscribers; but it will be apparent that it might beextended to include any desired number of subscribers. The incominglines are all brought upon the switchboard and are wired in multiple tocorresponding pairs of I it is our plan to employ in conjunction witheach switch a group of relays to perform functions which will behereinafter described, one group being provided for each switch, asillustrated in Fig. 3. Further, associated with each switch is a seriesof relays, (shown in Fig. 2,) which we will arbitrarily designateswitch-controlling relays, equal in number to the number of linesaccommodated in the exchange, all of the relays in a series beingconnected in multiple with the common switch and corresponding relays ofthe several series being connected inmultiple with the correspondingsubscribers lines to form what we term subscribers sets of relays, oneset for each subscriber. This arrangement may be clearly seen byreference to Fig. 2, wherein the switch-controlling relays S C R in anytransverse line form a series associated with one of the line-selectingswitches L S of Fig. 3, while thc'vertically-alining relays S C R formsets operatively connected with the corresponding subscribers lines L L&c. Further, associated with each subscribers linecircuit are certainprimary relays, each bridged from one side of the line to a groundinggroup of auxiliary relays and its series of the aforesaid switchcontrolling relays, is

identical with that of every other switch except in such particulars asmay be specifically pointed out. Hence the description of one line withreference to its associated devices will suffice as description of everyline, and, similarly, the description of one switch and its associateddevices will suffice as a general description of all of the switches.

In the drawings the parts are illustrated in the condition assumed whensubscriber No. 1 desiring to call subscriber No. 2, has taken thepreliminary steps necessary to secure the connection of his line withthe line of said subscriber No. 2 and has rung up said subscriber No. 2,the receiver of station No. 1 being illustratedas off its hook andproper relays of the central exchange being illustrated in the closed oractive position assumed to secure the connection of station No. 1 withstation No. 2.

Referring now to Fig. 2, it will be seen that with each incomingsubscribers line is associated a pair of primary relays, respectivelyindicated as P Rand P'Rand a set of switchcontrolling S C R, the numberof switch-con trolling relays corresponding with the number ofline-selecting switches employed in the exchange.

In Fig. 2 it will be noted that allof the primary relays upon the boardare connected to a common wire g, including in its circuit a commonlocal relay-battery LRB, and thence extending to groundat Ur. Further,it will be noted that one of the contact-points of each primary relay isconnected to the central-battery wire 5, which, as shown in Fig. 3, isconnected with the central batteryOB. The relay P R of each subscriberhas its other contact-point connected with the wire :r, which said wirehas certain connections, to be hereinafter described, with each of theswitch-eontrolling relays of the particular subscribers set, while theother contact-point of relay P R has a similar connection with thecompanion wire :11, likewise common to all the relays of a subscribersset. The relays P R and P R are preferably identical in construction,each preferably comprising simply an electromagnet the movement of whosearmature serves to bring into contact two normally open or separatedcontact-springs. In detail the connections of these two relays are asfollows: One terminal of the spool ofrelay P R is tapped by wire 17 toline-wire Z, and its other terminal is tapped by wire 18 to the wire 5One spring of the normally separated contact-springs is directlyconnected with wire :11, while the other is tapped, as indicated at 19,to the battery-wire 7). The relay P R also has one terminal of its spooltapped by wire 18 to the wire 9, its opposite spool-terminal beingconnected by wire 20 with the side! of the incoming line. One of thecontact-springs of relay P R is tapped by wire 19' to the commonbattery-wire b,and its other spring has direct connection with the wire:0. Groundreturn circuits may be established through the sides of thelines to include the spools of the respective relays, as will behereinafter fully described.

Referring now to the wiring of the switchcontrolling relays S O R, itwill be noted that all of the relays of a subscribers set have similarcontact connections with the sides l andl of the line of the subscriberand with the companion wires of the auxiliary circuitscc and Ir.Further, certain of the contact and spool connections of each relay in aseries corresponding with a switch are made to three pairs of wirescommon to the series and indicated as a a, c c, and (Z d, theconnections whereof will be hereinafter traced.

Referring now to the construction of the switch-controlling relaysillustrated, it will be seen that each relay comprises an electromagnetwhose armature is carried upon the extended leg of a T-shaped pivotedmember. Five contact-springs adapted for cooperation with correspondingcontact-points are carried by the armature-carrying member, one suchspring being carried by the extended leg, and the remaining four springsbeing arranged one on each side of each end of the cross-head of thearmature-carrying member. The armature is so arranged that when in itsnormal or unattracted position all of its contacts are open.

To simplify the drawings and description, it is believed unnecessary tonumber each of the contact-springs; but said springs will be referred toby their relative positions, the cross-head springs beingspoken of asupper Ls ht as v and lower, right and leftspr1ngs, and the singlesprings upon the extended legs of the armature-carriers being referredto as the end springs. The contact-points will be correspondinglydesignated.

To describe now the wiring of the switchcontrolling relays: One terminalof each spool is tapped at 21 to a wire 22, which is tapped to theauxiliary line a of a subscribers set of relays. The opposite terminalof the spool is tapped by wire 23 to the wire 0, common to a series ofthe relays. The wire 22 is likewise tapped by wire 2% to the lower rightcontact-spring of the relay and has a connection to the endcontact-point of the relay. The end contact-spring is tapped by wire 25to the wire 0, common to a series of relays. The lower rightcontact-pointis tapped by wire 26 to the wire (I of a relay series. Thelower left contact-point is similarly tapped by wire 27 to the wire (Zof the relay series. The lower left spring is tapped by wire 28 to theauxiliary wire 0:. The upper right and left contact-springs are tappedby wires 29 and 30, respectively, to the line-wires/and Z, respectively.The coacting contact-points, upper right and left, respectively, aretapped by wires 31 and 32, respectively, to the wires 11. and a,respectively, common to a relay series. These wires (6 a we willhereinafter refer to as "conncctingwires, as, together with another pairon continuing wires, they subserve practically the functions of the cordwires of a manual exchange.

Referring now to Fig. 3, it will be seen that with each line-selectingswitch L S is associated a group of three relays, similar in theirgeneral construction to the switch-controlling relays and which forpurposes of convenient identification we will arbitrarily designate forreference as the circuit-closing relay O O R, the key-controlled relay KO R, and the busy-test relay B T R. Further, each switch has anoperating-relay proper, S O R, having a spring on its armature normallycontacting with the upper one of two associated contact-points, and areleasing-magnet R M, movement of whose armature actuates a mechanicalswitch releasing device to be described. Each switch also has in theoperative relation thereto (best shown in Fig. 4) a set of threecircuit-changing springs, (indicated, respectively, by the numerals s1),s

and spi) a pair of circuit-making spring 579* and 8p, and a pair ofcircuit-breaking springs 8p and SP A power-driven ringing-generator forthe entire exchange is indicated at R, and a busy-test buzzer orvibrator of an ordinary type, likewise for the entire exchange, isillustrated at Z. O B represent a central battery common to the wholeexchange, while local batteries, one for each switch, are indicated at SR B and will be hereinafter arbitrarily designated switch-relaybatteries.

Referring now to the general plan of wiring, it will be seen that thepairs of wires a a, 0 c, and (Z (Z of the several relay series are ledinto proper connection with devices of the corresponding switches, suchconnections being hereinafter fully described. The corresponding relaysof the several groups are quite independent of each other; but theseveral relays of each group are similarly wired relative to each other.Certain common connections for the several groups of relays and switchesare, however, provided,the following-named wires being common to all theswitches and their associate devices in the exchange.

If indicates a battery-wire connected to the terminal of central batteryC B opposite that to which the battery-wire b is connected. 6 indicatesanother battery-wire tapped to wire 5 while 6 indicates a battery-wirecommon to relays of the several groups tapped to wire 5.

r and 0" represent wires connected with opposite terminals of theringing-generator R and having taps to like contacts of correspondingrelays of the several groups, while .2 and 2 indicate wires connectedwith the terminals of the buzzer Z and likewise tapped to contacts ofcorresponding relays of the several groups.

To take up now in detail the wiring of a single group of relaysassociated with a switch and the other mechanism of such switch, we willfirst trace the six wires (0 a, c 0', and (Zd. The wire a is connectedby a suitable split tap 39 to both the upper and lower left springs ofthe circuit-closing relay C C R and is also tapped by wire 40 to theupper right spring of the busy-test relay B T R. The wire a is tapped bywire 41 to a common connection 41 between the right upper and lowersprings of the circuit-closing relay O C R and from the point of saidtap extends through an impedance-coil l C to tap the wire I), connectedto the battery, as heretofore specified. The wire 0 is tapped by wire 42to the busy-test relay B T R, the tap being split and one branch, 43,connected with the lower right spring of said relay, while the otherbranch, 44, terminates in the end contact-point 45 of the busytestrelay. It will be noted, however, that the end contact-point 45 is sodisposed relative to its spring that it contacts with said spring whenthe relay is deenergized. In this point alone the busy-test relaydiffers in mechanical construction from the switch-controlling relays.From the point where the tap 42 is taken the wire 0 extends to andterminates in the circuit-closing spring 8p. The wire 0 is tapped at 46to one terminal of the spool of the circuit-closing relay G C R. Again,it is tapped by wire 47 to the lower left spring of the busy-test relayB TR. From the last-mentioned tap it extends to and is connected withthe wire 48, which forms the connection between one terminal of theswitchrelay battery S R B and the lower circuitchanging spring 512 Thewire l is directconnected to the lower spring 579" of the pair ofcircuit-making springs. The wire d is direct-connected with one terminalof the spool of switch-operating relay S O R.

Referring now to the circuit-closing relay 0 C R, the upper pair ofcontact-points are connected by wiper-wires w and on, which in operationare complementary to the connecting-wires a a, to the two wipers orcontactsprings of the operating-arm 101 of the lineselecting switch L S.The lower left and right contact-points are connected, respectively, bywires 50 and 51 with the left lower and upper springs of thekey-controlled relay K C R. The spool-terminal of the circuitclosingrelay opposite that connected by wire 46 with line 0 is connected towire 52, from which taps 53 and 54 respectively extend to the endcontact-points of the circuit-closing and key-controlled relays. The endcontactsprings of the three relays C C R, K C R, and B T R are allconnected together, being respectively tapped by wires 55, 56, and 57 toa common connecting-wire 58.

Examining now the connections of the key controlled relay K O R, notheretofore stated, the right upper spring is tapped by wire 59 to theringer-wirefl. The lower right spring forms a terminal for wire 60,which extends thence to one terminal of the spool of the busytest relayB T R and is tapped at 61 to the lower right contact-point of saidrelay. The upper right point of relay K C R forms a terminal of wire 62,connected with the other terminal of the spool of busy-test relay B T R,said wire being tapped by wire 63 to the lower left contact-point ofsaid busy -test relay. The two usual lower contacts for thelower rightand left springs of the key-controlled relay K G R are connectedtogether by wire 64. In addition to these usual contact-points anadditional contact-point 65, arranged for contact with the lower left'spring when the relay is denergized, is provided. A wire 66, terminatingat one end in said contact-point 65, includes an impedance-coil I G andis tapped to the battery-wire 6 One terminal of the spool of thekey'controlled relay K C R is tapped at 67 to the'battery-wire b, andits other terminal is connected by wire 68 with the upper contact-pointassociated with the spring carried by the armature of switch-operatingrelay S O R.

Referring now to the busy-test relay B T R, its upper left spring isconnected by wire 69 with the battery-wire 71 Its upper right spring istapped by wire 10 to the connectingwire a, as heretofore described. Thecoacting contact-points are tapped by wires and 71, respectively, tobuzzer-wires .2 and of the buzzer Z. The remaining connections of thebusy-test relay have been heretofore described.

Referring now to the connections of the switch mechanism proper, whichmay be-best seen in Fig. 1, the terminal of the operatingspool oppositethat connected to wire (1 is tapped by wire 72 to the battery-wire if.which, as heretofore stated, extends to the circuit-changing spring .91()ne side of the spool of the releasing-magnet R M is tapped by wire 7 3to the aforesaid battery-wire b and the other spool-terminal is wired,as indicated at '74:, to the lower contact-point of thearmature-carrying lever of the switch-operating relay. Thecontact-spring of said switchoperating relay S O R is connected by wire75 to the circuit-closing spring sp". The terminal of the switch-relaybattery S R B opposite that to which wire 18 is connected, as heretoforedescribed, is connected with the lower circuitbreaking spring s7) bywire 76. The upper circuit-changing spring s3) is connected by wire itwith the middle spring $1.2 of the circuit-changing group of the nextsucceeding switch, while the upper spring s1) of said second group issimilarly connected by wire it with the middle spring 512 of thecircuitchanging group of the third switch, and so on, it beingunderstood that a battery-wire b is connected to the central movablespring sp of a circuit-changing set for one switch and the upper spring81) of said group for each switch being wired to the spring .9) of thegroup of the next succeeding switch throughout the entire exchange. I

For purposes of illustration we have herein shown a simple form ofswitch which might be used in the practice of our invention, and themechanical arrangement of said switch we will now describe.

Referring particularly to Fig. 1, 101 indicates a rotary switch-armmounted upon a rotatable shaft 102. Said shaft likewise carries aratchet 103 and is connected with a spring 101, arranged to exert apressure upon the shaft, tending to hold it in the inactive positionillustrated in Fig. 1. The switcharm 101 is provided with twocontact-springs or wipers 105 and 105, adapted when the arm is moved tosweep over the corresponding pairs of contact-points s s &c., into whichthe incoming subscribers lines are led, as heretofore described. Theswitch-arm is also provided with two insulated projections 106 and 107,adapted when the switch is in inactive position to respectively engagethe springs s2) and A7). The spring .571 is held its projection 106 incontact with the lower spring sp of the circuit-changing set, but is soarranged that when released by the movement of the switch-arm it springsinto contact with the uppermost spring .572 of the circuit-changing set.The insulated projection 107 serves to hold the spring *7) out ofcontact with the spring sp",,such contact being made as soon as theswitch-arm is moved. 108 indicates the armature of the switch-operatingrelay S O R, mounted upon one end of a pivoted lever 109, the oppositeend of which extends into proximity to the ratchet 103. 110 indicates apawl pivoted on the free extremity of the lever 109 and normally held byaspringlll in engagement with the ratchet 103. 112 indicates a pin orlinger projecting from the pawl 110, so that when struck upward it willthrow the pawl out of engagement with theratchet 103. It will beapparent now that whenever the spool of the switch-operating relay isenergized to attract its armature the ratchet-and-pawl connection -willserve to rotate the shaft forward a distance corresponding with onetooth of the ratchet. The parts are so proportioned that this movementalso just sutlices to bring the wipers 105 and 105 into contact with thecorresponding terminals of the next preceding line, one movement of thelever serving to make connection between the wipers and the contacts s,two movements to move the wipers into contact with termini s &c.

The holding and releasing means may be arranged as follows: 113indicates a dog pivoted at 11% and provided, as at 115, with a toothadapted to engage the ratchet to prevent its return to inactive positionunder the tension of its spring 10-1. A spring 110 serves to maintainthe dog in operative or holding position. 117- indicates a lugprojecting from the dog 113 and normally lying immediately below theprojection 112 from a pawl 110. 118 indicates a pin projecting from thedog on the. same side of the pivot as the tooth 115. 119 indicates apivoted lever at one end carrying the armature of the release-magnet R Mand at its other end carrying a pivoted releasing-arm 120. The arm 120extends up beside and overlies the dog 113, its front edge normallyresting in contact with the pin 118, carried by said dog, and a linger125, projecting from the switch-arm. A spring 121, connected to a hook122 of the arm 120, projecting on one side of its pivot-point, serves toboth hold the arm normally down in contact with the stop122 and tomaintain its bearing with a constant pressure against the stud 113.Notches 123 and 121 are provided on the side of the arm 120, saidnotches being so arranged that when said arm 120 is elevated and movedinward the pin 118 of the dog and the end,of the circuit-breaking spring.s}) respectively rest therein.

The operation of the release mechanism so ITO arranged will be asfollows: When the spool of the magnet R M is energized to attract thearmature carried by lever 119, the arm 120 will be raised. If now theswitch-arm 101 be in advanced position, so that the finger 125 isremoved from the path of the arm 120, the last said arm will be movedinward by the tension of its spring 121, so that its notches 123 and 124respectively engage the pin 118 and the end of the spring 571 WVhen nowthe magnet is deenergized, the spring 121 pulls down the arm 120,holding it constantly, however, toward the engaged stud and spring andpulling with it the said instrumentalities. Consequently any circuitestablished through springs .92 and .59) will be broken, and the dog 113will be moved so that its tooth 115 is dis engaged from the ratchet 103.At the same time projection 117 of the dog strikes the projection 112 ofthe pawl 110, throwing the pawl out of connection with the ratchet. Theratchet being now entirely freed, the shaft rotates to return the arm101 to its normal position under tension of the spring 104. When the arm101 reaches its normal or inactive position, its linger 125 strikes thearm 120 of the release mechanism and moves it to the right against thetension of its spring, thereby releasing the stud 118 of the dog 113 andspring .592 from the engaging notches in the arm 120 of the releasemechanism. At the same time the projection 117 of the dog is removedfrom the path of the projection 112 of the pawl, allowing the pawl toreturn under tension of its spring 111 into engagement with the ratchet.The parts are now restored to their initial position, as illustrated inFig. 4

Having thus described minutely the present illustrative embodiment ofour invention, we will now describe the operation of the system.Assuming that the subscriber at station No. 1 is desirous of callingsubscriber No. 2, his actions and their results will be as follows: Theremoval of the receiver 6 from the hook 5, as indicated at station'No. 1in Fig. 1, cuts the bell 8 out of the line and the telephone instrumentsinto operative connection with the two line-wires, the circuitstherethrough being traced in through line-wire Z, key 9, wire 11 to key11, thence by wire 13 to the transmitter 7, through the primary 7) ofthe induction-coil to the receiver-hook 5, and thence by wire 16 and key10 back to the line-wire Z. Now the primary impulse-key 9 is depressedby the calling-subscriber, grounding the side of the line Z through thewire 12. A circuit is thereby completed, which we may trace from theground in Fig. 1 through the primary impulse-key 9 to the wire Z,thence, in Fig. 2, by wire 17 to the spool of primary relay P R, backfrom the spool of said relay by wire 18 to the wire 9, and by said wirethrough the local battery L R B to ground. It will be noted that theabove circuit includes the spool of the primary relay P R, the armatureof which is accordingly attracted, closing its associatedcontact-springs. This establishes a circuit which may be traced from thelower spring of primary relay P B through wire 19 to the battery-wireZ), which, it will be remembered, connects with left end of the centralbattery C B (shown in Fig. 3) and, on

the other hand, extending from the upper spring of the relay P R by wirein and wires 22 and 21 to the spool of the first switch-controllingrelay S C R of the first subscribers set, thence from the other terminalof the spool by tap 23 to wire a, continuing, on Fig. 3, past taps 46and 47 to the wire 48, thence upward to the lower spring 8[)3 of thecircuitchanging set, which (it being assumed that the uppermost switch LS is not in use) contacts with spring s7) and from the latter spring bybattery-wire Z) to the right terminal of the central battery C B. Thusit will be seen that a closed circuit is established which includes thecentral battery C B and the spool of the first switch-controlling relayS C R. The armature of said relay S C R-is accordingly attracted to theposition illustrated in Fig. 2, and a local circuit, including thespool, is established to hold the armature indefinitely in closed oractive position. The local circuit is traced as follows: from the endcontact-point of the relay by wires 22 and 21 to the spool, thence bywire 23 to the series wire 0, thence continuing on, in Fig. 3, to thewire 48, connected to the left side of the local switclrrelay battery SB B. On the other hand, the circuit extends from the end spring of therelay by wire 25 to series wire 0, thence, in Fig. 3, alongto the springsy), which is closed upon spring 72 and thence by wire 76 to the rightterminal of the switch-relay battery S R B, completing the closed localcircuit. It will be noted that as long as the subscriber maintains theprimary impulse-key 9 in closed position the spool of theswitch-controlling relay S G R will be energized both by the centralbattery C B and the local battery S B B. It is necessary, therefore,that the wires 48 and b be connected to like terminals of the twobatteries to prevent the occurrence of a short circuit. It willbeunderstood, however, that the primary impulse-key 9 need be closedonly momentarily to send a single impulse through the primary relay PRand may be then released. The switch-operating key 10 is now depressedby the calling subscriber a number of times corresponding with thenumber of the subscriber whom he desires to call, in the presentinstance two movements of the key being necessary to call subscriber No.2. Upon each depression of the key 10 a circuit is established throughthe primary relay P R as follows: from the ground, in

Fig. 1, by wire 12 and tap 10 to key 10,

thence to the line-wire Z, continuing on, Fig. 2, by the tap 20 to theone side of .the spool of'relay P R, thence by wire 18 to wire r throughthe local battery L R B, and to ground again. Consequently the armatureof relay P R will be now attracted to close its contact-springs as manytimes as the switch-operating key 10 is depressed. ith each movement ofthe armature of said relay P R a circuit is closed through the spool ofthe switchoperating relay S O R as follows: beginning at the upperspring of the contact pair of the relay P R by wire a" and tap 28 to thelower left spring of the switch-controlling relay S ,C R, (which, itwill be remembered, is being maintained in active position,) thence bytap 27 to wire (7, which continuing (in Fig. 3) extends direct to thespool of the relay S O R, thence back by wire 72 and battery-wire b tothe right side of central battery C B, and, on the other hand, from thelower contactspring of the primary relay P R by tap 19 to thebattery-wire 7), connecting with the opposite terminal of centralbattery C B. It will thus be apparent that the spool of theswitch-operating relay SD R will be energized and deenergized as manytimes as the switch-operating key 10 of the subscribers station may bedepressed.

Referring now to Fig. 4, it will be apparent 1% of the line L coming infrom the station of subscriber No. 2. In Fig. 3 the wiper-arm isillustrated in such position. The movement of the arm 101, as heretoforestated, releases the spring 6P2, which leaves its lower spring 5]) andcontacts with spring for a purpose to be described. It will be noted nowthat the line-wires of subscriber No. 1 are connected, respectively, bytaps 29 and 30 to connecting-wires a and H, which, as shown in Fig; 3,are led in by taps 11 and 39, respectively, to the right upper and lowerand left upper and lower springs of the circuit-closing relay 0 U R. Itwill also be noted that the wipers of a switch arm are connected bywiper-wires and w to the upper left and right contact-points of saidcircuit-closing relayU C R. As no circuit has yet been establishedthrough the spool of said relayG O R, however, the lines of thesubscribers 1 and 2 are not yet connected, but are open at that point. Asingle operation upon the part of subscriber No. 1 now secures for himthe connection of the two lines and either rings subscriber No. 2 or, ifthe latter subscribers' line be busy, gives the calling subscriber No. 1the busy slgnal and disconnects h1s line from the line already busy. Theresults enumerated follow the depression of the connectn'ig-key 11,which closes a local circuit through the primary relay P R as follows:from the ground by wire 12 through the connecting-key 11, wirell, andkey 9, to thelinewire 1, thence by tap 17 to the coil of relay PR, backby tap 18 to the ground-wire g, and thence through the local battery L RB to ground at G. As long as the said connectingkey 11 is maintainedclosed the armature of the primary relay P R maintains connectionbetween the springs of said relay, establishing the following circuit:from the lower contactspring of relay P R by wire 19 to the batterywireI), connected to the left-hand side of the central battery C B, and. onthe other hand,,extending from the upper spring of the pair of relay 1 Rby wire a and taps 22 and 24 to the lower right spring of theswitch-controlling relay, thence by tap 26 to wire (Z, thence direct tospring x79 on to the upper spring x7), thence by wire 75 to the springof the switchoperating relay S O R, (which is now deenergizcd,) and fromsaid spring by wire 68, through the spool of key-controlled relay K C R;thence by tap 67 to the battery-wire 7/, which connects with the rightterminal of the central battery C B. Accordingly the relay K C R isenergized, attracting its armature and closing its various contacts. Itwill be apparent, however, that the relayK C R remains energized onlywhile the keyll is held depressed. The closing of the key-controlledrelay K C R primarily serves to close a circuit through the spool ofcircuit-closing relay C (1 R, such circuit being traced as follows: onthe one hand, from the end spring of the relay K C R by wires 56 and 58to end spring of relay B T R, end spring-contact 45, wire 14, and tap 12to the wire 0, through the springs s and .sp? and wire 76 to the rightend of the battery S R B, and, on the other hand, from the endcontact-point of relay K C R, tap 54K, wire 52, to the spool of relay 0C R, thence from the other side of the spool by tap 46, wire 0, and wire18 to the left end of battery S R B. The armature of relay C C R isaccordingly attracted and is held in such position irrespective of thekey controlled relay by the closing of the end spring of the relay C C Rupon its point, giving a connection (through wires and 53) between wires58 and 52 of the circuit last traced parallel with the connectionbetween such circuit-wires 58 and 52 established by the keycontrolledrelay through wires 5st and 56. The closing of the circuit-closing relayserves, primarily, to establish a direct connection between the lines ofthe calling and called subscribers, including no local resistances, suchas relay-coils or like impedanccs', within the line-circuit in theexchange. Further, the closing of said relay serves to bridge the aringer, buzzer, and central-battery wires onto the connected lines, sothat upon the closing of circuit through any one of saidinstrumentalities it is enabled to perform its functions. The ringingand busy-signal ing devices are first brought into operation only ifboth the key-controlled relay K (J R and circuit-closing relay aresimultaneously closed, while the central battery is bridged onto theconnected lines only when the relay K C R is denergized. WVe will firsttrace the line-circuit through from station to station, presuming thatthe station instruments are in the conditions illustrated in Fig. 1 ofthe drawings. Commencing now with the hook 5 at station 1: by wire 13,including primary 7) of the induction-coil, and transmitter 7 to theupper contact of the connecting-key 11, thence through the key 11, wire11, and key 9 to the line-wire Z, continuing, Fig. 2, to the energizedswitch-controlling relay by tap 30 to the upper left spring thereof,thence by tap 32 to connecting-wire a, continuing, Fig. 3, to thecircuit-closing relay 0 U B, through tap 39 and upper left spring,thence by complementary connecting-wire .w to the wiper, and on to theterminal of line L, corresponding with line-wire Z, thence (returning)through wire Z of pair L in Fig. 2 up to station 2 in Fig. 1, in throughthe key 9, wire 11", key 11, wire 13, and tap 1 1, including the bell 8,to the receiver-hook 5, out over wire 16 and key 10 to line Z, returningto the corresponding terminal of the central switch, through the wiperto wire 20, onto upper right spring of the relay C C R, thence by taps4:1 and 11 to the connecting-wire a, back to the upper right spring ofthe energized switch-controlling relay S C R, and by tap 29 to line-wireZof line L and in through key 10 and wire 16 of station No. 1 to thereceiver-hook 5. Assuming now that the key 11 is, when depressed toenergize the key-controlled relay K CR, as heretofore described,maintained in such position for a suitable time, the ringing-generator Ris bridged upon the connected'lines of subscribers 1 and 2 to ring thebell of subscriber 2 and energizing the primary 7) of the induction-coiland the transmitter of subscriber No.

1, the circuit being as follows: from one'terminal of the generator bywire r and tap 19 to the upper-left spring of the key-controlled relay KC R, thence by wire 51 to the lower right spring of thecircuit-closing,relay C C R, which, it will be remembered, forms part ofthe connection of one side of the line of subscribers 1 and 2. From theother terminal the circuit is traced from the ringing-generator B,through 'wire '1", wire 59, to upper right spring of the key-controlledrelay K C R, thence by wire 62 to the spool of the busy-test relay B TR, returning by wire to the lower right spring of the key-controlledrelay, thence by the connection 64 to the lower left spring, and

' thence by wire 50 to the lower left contactwill be seen that theringer is bridged on the two lines, so that it transmits its impulsesboth ways. In tracing the foregoing circuit it will have been noticedthat the spool of the busy-test relay B T R was included therein. Itwill be understood, however, that the said spool is so wound that itsarmature is not responsive to the current supplied by theringing-generator, which for purposes of illustration we will say-isdesigned to develop about one-tenth ampere, but that said armature isresponsive to a heavier current of, say. onefifth ampere. designed tofurnish a tenth ampere of current with the working resistance (which mayby proper balancing of the lines be made uniform for all subscriberslines) it will be apparent that if a circuit be established to con-'neet both the battery and the ringing-generator to jointly supplycurrent to the spool of the busy-test relay the latter will be energizedto attract its armature when the directions of current from both sourcescoincide. Assuming now that line calledthat is to say, the line ofsubscriber No. 2-is already busy, it is obvious that any circuit closedacross the wiper-lines w and 10 will receive the batterycurrentfromthebusyline. If now the key-controlled relay is actuated to bridge theringinggenerator across the connected lines of the subscribers by thecircuit including the spool of the relay, as above described, it will beapparent that current from both the central battery and the generatorwill pass through the spool of the busy-test relay. Consequently thebattery-current of, say, one-tenth ampere is alternately reinforced andopposed by the impulses generated by the ringing-generator, so that apulsating current of one-fifth ampere is developed in the relay-spool.Consequently with the first such impulses the armature of said relay isattracted, breaking the circuiteontrolling relay-circuit as the endcontactspring of the relay leaves its point 45, and so by therestoration of the circuit-controlling relay to inactive positionbreaking the ringing-circuit. The busy-test relay is now maintainedclosed by a local circuit, which may be traced from the spool of therelay B T R by wire 60 and tap 61 to lower right contactspring, thenceby wire 43 and tap 12 to wire 0, thence through the circuit-makingsprings .93) and .571 to the right side of the local relaybattery S R B,returning by wire 18, wire 0, tap 4E7, lower left spring of relay B T R,tap 63, and down by wire 62 to the opposite side of the spool of relay BT R. It is well known that when an electromagnet is once energized toattract its armature but little current is required to retain thearmature in attracted position, and the local battery need not be ofgreat strength to accomplish this result. The actuation-of the busy-testrelay B T R in breaking the ringing-circuit by moving its endcontact-spring from contact-point 45 also de- If the central battery bealso Ioo IIO

stroys the connection between the two subscribers connecting-lines, asit will be recalled that the local circuit maintaining thecircuitclosing relay C U R in energized condition included therein saidspring and point of the busy-test relay, so that said local circuit isbroken by the actuation of the said busy-test relay. In addition to itscircuit-breaking functions the busy-test relay also serves to bridgeupon the line of the calling subscriber the busy vibrator or buzzerZ.The buzzer-circuit, it will be seen, is made direct through wire son theone side to upper right spring of the busy-testrelayBTR and thence bytap 4:0 to the wire a, while on the other side it includes line 2, upperleft spring of the busy-test relay, tap 69, battery-wire 6 which istapped to the battery-wire I), and thence through the central battery (JB, returning by the opposing battery-wire 6 up to the point where saidwire is tapped by wire it, thence through the im pedance-coil l G, andreturning along the wire a; It will be remembered that theconnecting-wires 1 and a are connected at the switchcontrolling relay SC R by taps 32 30 and 31 29, respectively, with the subscriberslinewires and Z, and it will there fore be apparent that a circuitincluding the central battery C B and the vibrator Z will be bridgedupon the calling-subscribe1"s line. It may here be noted that when oncethe busy signal is start ed it continues indefinitely, irrespective ofwhether the line desired remains busy or not, until the callingsubscriber takes proper steps to restore the whole system to normalcondition, and the contact at point 45 of relay B T R remaining brokenthe calling subscriber is unable to actuate the circuit-closing relay CC R for any purpose.

Referring now for a moment to the ringing operation heretoforedescribed, when the ringing-generator is bridged upon the connectedlines of two subscribers it will be obvious that an arrangement wherebythe calling subscriber is apprised of the fact that the calledsubscriber is being rung may be advantageously employed. We provide,therefore, a closed circuit through the calling-subseribefis line andthe primary winding of his induction-coil in order that the alternatinggenerator-current flowing therethrough may inductively occasion themagnet in his receiver to assume alternately opposite polarities,causing its diaphragm to vibrate with a series of clicks, assuring himthat his line is working properly and the desired party is being called.It will be remembered that in ringing the connecting-key 11 isdepressed, and With such understanding the circuit may be traced fromthe line Z, through the key 9, wire 11", to connecting-key 11, thence tothe second contact-point of said connecting-key, and by tap 15 throughthe resistance 15 (if included) and wire 13 to the transmitter andprimary of the induction-coil to the upper hook-contact,

and key 10 to the line Z. It is essential that in this circuit justtraced there be considerable resistance, for reasons to be hereinafterstated, and the inclusion of the resistance 15 will only be necessarywhen the resistance of the transmitter 7 is insuflicient for the purposeto be disclosed. Assuming now that the called subscriber is not busy,but that the ringing operation has been concluded and the key 11released by subscriber No. 1, the system is in the condition illustratedin the drawings, the circuit-closing relay C U R being'closed and thekey-controlling relay K C R being open. Now it will be apparent that thecentral battery C B is bridged upon the connected-subscribers lines, asin an ordinary central-energy exchange. The circuit in detail is asfollows: starting from the left side of central battery C B, bybattery-wire I) and wire 6 tapped thereto. through taps 66, includingthe impedance-coil l C, to lower left spring of relay K C R, thence bywire 50 to the lower left spring of relay U U R, and by tap 39 onto theside (0 of the pair of connectingwires. On the other hand, starting fromthe right side of the battery, the circuit is traced by battery-wire I)direct to wire a, the latter wire including the impedance-coil l C andforming part of the remaining side of the connecting pair of wires. Nowto complete the talking-circuit it only remains for the subscriber atstation No; 2 to remove his receiver from the hook, cutting histransmitter and induction-coil primary into circuit, as heretoforedescribed.

It will be noted from the foregoing statement of operation that the lineof the calling subscriber is not directly connected to the wipers of theswitch until the operation of actuating the switch-arnito advance it tothe terminal contact-points of the line of the subscriber desired to becalled has been accomplished and the lines prepared for the final stepof ringing the called subscriber or notifying" the calling subscriberthat the line desired is busy. Further, it will be noted that theoperation of connecting the line of the calling subscriber with thewiper is performed by an instrumentality distinct from that employed inoperating the switch. This arrangement results in many distinctadvantages, as it is apparent that entire secrecy is insured any twosubscribers engaged in conversation, as the now calling subscribercannot have his line bridged upon the connected lines before he operatesthe connecting-key and as soon as his connecting-key is depressed hewill get the busy-signal and the momentary connection of hisconnecting-wires with the wiper-wires will be broken. Further, such anarrangement obviates the possibility of calling subscriber by anyimproper manipulation of his actuating devices from bridging the ringinggenerator upon the wiper-line and then in acthencereturning through thehook 5, Wire 16,

tuating the switch, momentarily connecting said ringer with each of thelines over which its wiper-contacts travel.

When the connected subscribers have finished their conversation and itis desired to restore the switch and the other instrumentalities totheir normal or inactive positions, the keys9 and 11 are simultaneouslydepressed and both maintained closed for an instant. As a resultcircuits are established as follows: Both line-wires land Z beinggrounded by the depression of the keys a ground return-circuitisestablished through each of the primary relays PR and P R, as heretoforedescribed. Consequently the contact-springs of relay P R are broughttogether, establishing a circuit, which has heretofore been traced,through the central battery C B,the spool of the switchoperating relay SOR, and back by way of the lower left spring of the switch-controllingrelay S CR and the auxiliary line as. The armature of theswitch-operating relay being attracted, its end spring is brought downinto contact with the lower contact-point, and .(the relay P R beingenergized and its contactsprings accordingly connected) the attractionof the armature of the switch-operating relay establishes a circuitwhich may be traced from the upper spring of the relay P Rby the line00, through the lower right spring of the switchcontrolling relay S C Rby tap 26 to wire cl, thence up to the lower spring 819 of thecircuit-closing pair of the line-selecting switch, by wire to the endspring of the switchoperating relay, lower contact, and wire 7 1, to thespool of the release-magnet, returning by tap 7 3 to the battery-wire bthence to the right end of the battery, and from the left terminal ofthe battery, by wire 5 and tap 19, to the lower spring of the primaryrelay PR. The release-magnet is accordingly energized, and thereleasing-arm 120 is raised to operatively engage the stud 118 of theswitch-armretaining dog 113 and the contact-making spring .519 asheretofore described. When now the keys 9 and 10 are released, thereleasemagnet is deenergized and, as heretofore described, frees theswitch-arm 101, sothat it is enabled to return under tension of itsspring 104 to inactive position while the circuitbreaking springs s1)and 810 are parted, so destroying the continuity of the. local circuitsserving to maintain the switch-controlling relay S C R and thecircuit-closing relay COR energized. Consequently all of theoperating-circuits being now broken the parts are all restored .to theirnormalor inactive positions, the return of the switch-arm serving, asheretofore described, to disengage the releasingarm 120 from the dog andthe springand permitting the return of these mechanicalinstrumentalities to their normal position.

Reverting now to the description of the wiring of the stations wherebythe calling subscriber is apprised of the fact that the ringof line L isactuated.

ing operation is being successfully consummated, it will be noted thatthe connections are such that ground-circuitsfor both primary relay P Rand P R are established. The path from line-wire Z (with which relay P Ris connected) to ground through key 11 has been fully traced; but itwill be noted that during the time the connecting-key 11 is depressedthe'line-wire Z (connected with relay P R) is grounded through key 10,wire 16, hook 5, line 13, (including coil 1) and trans mitter 7,) wire15, (with resistance 15, if present,) key 11, wires 11 and 12 to ground.The last-described restoring operation does not follow from thisconnection, however, on account of the high resistance interposedbetween relay P R and ground. The circuit just traced contains thetransmitter 7 and coil 1), which in most cases sufiice to prevent theflow of sufficient current through relay P R to attract the armature tosaid relay. Obviousl y, however, enough resistance may be included at 15to prevent the possibility of the relay P" R becoming operativelyenergized, and so inopportunely working simultaneously with relay P R torestore the devices to inactive position.

The foregoing statement of operation is predicated on the assumptionthat the call is made and connection established on a switchboardwhereon no lines are busy; but let us now assume that with lines L and Lconnected subscriberNo. 3 desires to call subscriber No. 5. Of coursethe personal operations of subscriber 3 are just as described inconnection with subscriber No. 1 and the relay P R The relay S O R ofthe first or upper series cannot, however, respond, as the primaryactuating-circuit of all of the relays in said series, it will beremembered, included a path across the springs .912 and s3] dependentupon the closed condition of the latter. The springs .319 and .939 ofthe first switch being parted when the switch is in use, as heretoforedescribed, prevents positively the completion of an actuating-circuitfor any relay of the first series. A corresponding primaryactuating-circuit traced.

through the second series, however, shows the lower spring cp to beclosed on the middle spring .539 which is connected through wire h,springs .91) and .912 of the first or upper switch with the battery-wire6 Any one of the switch-controlling relays of a series, it will beremembered, controls both the ener- ICO gizing-circuit of theswitch-operating relay of such switch and the connection of the callingsubscribers line with the connectingwires (0 a of the series. Thus everysubscriber when using a switch is protected against interference, theswitch-controlling relays of the corresponding series being absolutelyremoved from the control of any other subscriber, while the series ofswitchcontrolling relays corresponding with the first then idle switchare automatically brought within the control of any other subscriber.

For purposes of a full disclosure of our invention we have illustratedand described in some detail an embodiment thereof which we deemsuitable for illustration; but we do not desire to be understood aslimiting ourselves to such disclosure in detail, as our inventioncontemplates a broad system susceptible of many variations in specificembodiment without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim as new, and desire tosecure by Lettcrs Patent of the United States, is

1. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a central group of line-selecting switchesadapted and arranged to be instrumental in connecting for communicationthe lines of any two subscribers, switch-actuating means operativelyassociated with each switch, such means, for each switch, including aseries of devices each adapted and arranged to control the correspondingswitch, one of such devices in each series being operatively associatedwith each subscribers line for control by the subscriber.

2. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a central group of line-selecting switches,each adapted and arranged to be instrumental in connecting forcommunication the lines of any two subscribers, switch-actuating means,including a switch-circuit, and a series of switch-oircuit-controllingdevices, operatively associated with each switch, one of suchcircuit-controlling devices of each series being provided for andoperatively associated with each subscribers line, and means within thecontrol of each subscriber for operating the switch-circuit-controllingdevices associated with his line.

3. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a central group of line-selecting switcheseach having terminal contact connections with allof the lines and eachhaving also a movable member adapted to be brought into contact with thecontact-terminals of any line, and adapted and arranged to beinstrumental in connecting for communication the lines of any twosubscribers, means, for each switch, for actuating the movable memberthereof, and a series of devices associated with each switch adapted andarranged to control such actuating means, one such controlling device ofeach series being operatively associated with each subscribers line forcontrol from the subscribers station.

4. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a central group of line-selecting switches,each having terminal contact connections with all of the lines and eachhavingalso a movable member adapted to be brought into contact with thecontact-terminals of any line, means associated with each switch foractuating the movable member thereof including a circuit and a series ofcircuit-controlling devices, one device in the series for each switchbeing operative] y associated with each subscribers line for controlfrom the subscribers station and each device comprising circuitclosingmeans, and normally open circuit connections between the line of eachsubscriber and the movable contact member of eachlineselecting switch,each of said open circuits being adapted and arranged to be closed bythe circuit-closing means of the switch-controlling device of thecorresponding subscribers line included in the actuating means of thecorresponding switch upon the actuation thereof,

,to connect any subscribers line to the movable contact member of anyswitch.

5. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a central group of line-selecting switches,each switch having a set of terminals to which all of the lines arerespectively connected, and a contact member adapted to make contactwith the terminals of any line, means for establishing connectionbetween any two lines through said switch-contact member includingseries of switch-controlling relays, one series being operativelyassociated with each switch and each series having a relay operativelyassociated with each subscribers line for control from the subscribersstation, and suitable circuits for the relays.

6. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a central set of line-selecting switches,each switch having contact-terminals connected with each line and amovable contact member adapted to contact with the terminals of anyline, and adapted and arranged to be instrumental in connecting forcommunication the lines of any two subscribers, means associated witheach switch for actuating the moving contact member thereof, such meansfor each switch comprising a series of relays each adapted to controlthe corresponding switch, one of such relays in each series beingassociated with each subscribers line for control by the subscriber,means for placing the relays of one switch normally within the controlof all subscribers, and means for automatically removing the relays ofeach actuated switch from the control of any other than the actuatingsubscriber, and placing the relays of the first then idle switch withinthe control of such other subscribers.

7. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a central set of line-selecting switches,each having a series of contact-points forming terminals of all thesubscribers lines, and a movable contact member, means for actuatingsaid contact member including an electric circuit, a series ofswitch-controlling relays for each switch, each relay being arranged andadapted to control the circuit of the actuating means of its switch,means Within the control of each subscriber for actuating aswitch-controlling relay of each series, and means forautomaticallyremoving the relays of the first-actuated switch from the control of anyother than the actuating subscriber and placing within the control ofsuch other subscribers the relays of the first then idle switch.

8. In an automatic-telephone-exchange system, the combination of thelines of the subscribers, a plurality of switches each adapted andarranged to be instrumental in connecting the lines of any twosubscribers, means for actuating each switch, a series of relays foreach switch, each relay being adapted and arranged to control theactuating means for its switch, one relay of each series being providedfor and operatively associated with the line of each subscriber, anormally open circuit normally including one series of relays, meanswithin the control of each subscriber for closing said circuit to renderoperable the switch-actuating means of the switch corresponding withsaid series, and means controlled by the switch, for cutting out of thenormally open circuit the series of relays of the first-actuated switch,and cutting into said normally open circuit the relays of the first thenidle switch.

9. In an automatic-telephone-exchange system, the combination with thelines of the subscribers, of a plurality of line-selecting switches,each adapted and arranged to be instrumental in connecting forcommunication the lines of any two subscribers, actuating means for eachswitch including a normally open circuit, a series of switch-controllingrelays associated with each switch, each relay being adapted to closesaid actuating-circuit, and a relay of each series being provided forthe line of each subscriber, and an auxiliary circuit including meanswithin the control of each subscriber for energizing the subscribersswitch-controlling relay of the series of relays associated with anyswitch whereby the actuation of the corresponding switch is broughtwithin the control of the subscriber.

10. In a telephone-exchange system, the combination with the lines ofthe subscribers, of a line-selecting switch having a series ofcontact-terminals to which the subscribers lines are respectivelyconnected, and a contact member adapted to make contact with any of saidterminals, actuating means for said contact member including a normallyopen circuit having therein devices within the control of anysubscriber, adapted and arranged when the circuit is closed to actuatethe switch, a series of relays for said switch, one relay being providedfor the line of each subscriber, circuit connections for the lines ofthe respective subscribers and the contact member of the switch open atthe respective relays and adapted to be closed by the energizing of anyrelay to bring the switch within the control of the correspondingsubscriber, a normally open relay-energizing circuit, and means withinthe control of each subscriber for closing said circuit through hiscorresponding relay.

11. Incombination,apluralityoftelephonelines, a switch having contactsarranged to form the termini of the lines, and a contact member adaptedto sweep over said termini, electromagnetic devices for operating saidswitch, a circuit for the electromagnetic devices, a series of relays,one for each subscribers line, arranged to control the circuit of theswitch-actuating electromagnet, connectingwires arranged and adapted tobe connected to any line by the actuation of its relay, complementaryconnecting-wires terminating in the contact member of the switch, arelay adapted when energized to connectsaid complementary wires, andmeans associated with the switch arranged to be brought into operationby the movement of the latter for bringing the circuit-closing relaywithin the control of the subscriber, whereby the talkingcircuit may beestablished by the subscriber.

12. In combination,a plurality of telephonelines a line-selecting switchprovided with a contact member adapted and arranged to be instrumentalin connecting for communication the lines of any two subscribers, meansfor operating said switch-contact member arranged for control by anysubscriber, and means for connecting the line of the calling subscriberwith the switch-contact member arranged to be operated subsequently tothe switch-operating means. I

13. In an automatictelephone exchange system, the combination with thesubscribers lines adapted to be connected, and means for supplyingenergy to said lines when'connected for conversation, of means withinthe control of each subscriber for connecting any two subscribers lines,a ringing-circuit includinga ringing-generator adapted to be connectedto the connected lines of the subscrib-- ers, whereby when the calledline is busy and already energized current from the energized line isreceived in the ringing-circuit, a busytest circuit including asignaling device and means for connecting said device with the line ofthe calling subscriber, comprising a relay having its coil arranged toreceive current from the ringing-circuit, said relay being inoperable bythe ringing-generator current, and operable by the current transmittedthereto when said ringing-circuit isconnected to a busy line.

In testimony that we claim the foregoing as our own We aflix oursignatures in presence of two witnesses.

JOHN K. NORSTROM. HENRY M. GRAIF. In presence of GEO. T. MAY, Jr., MARYF. ALLEN.

